switch / case

The switch statement compares a single value against a list of exact constant candidates and jumps to the matching case. It is a clean alternative to a long else-if ladder when every branch is checking the same variable for equality against a specific value.

Basic Syntax

#include <stdio.h>

int main(void) {
    int day = 3;

    switch (day) {
        case 1:
            printf("Monday\n");
            break;
        case 2:
            printf("Tuesday\n");
            break;
        case 3:
            printf("Wednesday\n");
            break;
        default:
            printf("Some other day\n");
            break;
    }
    // Output: Wednesday

    return 0;
}

Execution jumps directly to the case label whose constant matches the switch expression. The optional default label runs when no case matches; it can appear anywhere in the switch but is conventionally placed last.

Fallthrough and Why break Is Required

Unlike many other languages, C does not automatically stop after a matching case's block finishes. Execution "falls through" into the next case's code, running it too, unless you explicitly stop it with a break statement.

int n = 1;

// BUGGY: missing break statements
switch (n) {
    case 1:
        printf("one\n");   // prints
    case 2:
        printf("two\n");   // ALSO prints -- falls through from case 1!
    case 3:
        printf("three\n"); // ALSO prints -- falls through from case 2!
        break;
    default:
        printf("other\n");
}
// Output:
// one
// two
// three

Warning

Forgetting break is one of the most classic bugs in C. Every case block that should not continue into the next one needs its own break (or a return if inside a function). Compilers such as GCC/Clang can warn about suspicious fallthrough with -Wimplicit-fallthrough — treat that warning seriously.

Intentional Fallthrough: Grouping Cases

Fallthrough is occasionally useful on purpose: stacking multiple case labels with no code between them lets several values share the same block.

char grade = 'B';

switch (grade) {
    case 'A':
    case 'B':
    case 'C':
        printf("Passing grade\n");
        break;
    case 'D':
    case 'F':
        printf("Failing grade\n");
        break;
    default:
        printf("Invalid grade\n");
        break;
}
// Output: Passing grade

Note

When fallthrough is intentional and spans actual code (not just stacked empty labels), it is good practice to add a comment such as /* fallthrough */ so future readers know it is not a forgotten break.

switch Only Works on Integer Types

A genuine limitation of C's switch: the controlling expression and every case label must be a constant integer expression — that includes int, char, and enum values. C has no built-in support for switching on strings, unlike some other languages that do allow string switch statements.

char *name = "bob";

// This does NOT compile in C: you cannot switch on a char* / string.
switch (name) {
    case "bob":     // ERROR: case label does not reduce to an integer constant
        printf("Hi Bob\n");
        break;
}

// Correct approach: use if/else with strcmp() instead.
if (strcmp(name, "bob") == 0) {
    printf("Hi Bob\n");
} else if (strcmp(name, "alice") == 0) {
    printf("Hi Alice\n");
}

Warning

Do not try to switch on a char *. C compares strings by content, not by a single machine value, soswitch cannot dispatch on them at all. Use an if / else if ladder with strcmp() (from <string.h>) instead.

Feature	C switch
Valid controlling types	int, char, enum (any integer-promotable type)
Switching on strings	Not supported
Falls through by default	Yes -- break is required to stop
Multiple values, one block	Stack case labels with no code between them
Unmatched value	default label runs if present, otherwise nothing runs

Key Points

switch compares one value against a series of exact constant case labels.
Without break, execution falls through into the next case -- this is one of the most classic C bugs.
Stacking case labels with no code between them is the correct way to group values that share behavior.
switch only works on integer-compatible types (int, char, enum); it cannot switch on strings.
For string comparisons, use an if/else ladder with strcmp() instead of switch.